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Classification:

Melanostoma scalare belongs to the subfamily Syrphinae, tribe Bacchini.

Distribution:

From Iceland and Fennoscandia south to Iberia, the Mediterranean and North Africa; from Ireland eastwards through most of Europe into European parts of Russia; in Siberia from the Urals to the Pacific coast (Kuril Isles); in eastern parts of the Afrotropical region south to Zimbabwe; throughout the Oriental region to New Guinea.

Habitat:

Humid and mesophilous forests, also in open terrain with bushes.

Description:

Body length: 7 - 9 mm; face with shiny central hump, mostly dusted; arista with short hairs.
Male: abdomen remarkably long and narrow with mostly 3 red-yellow patch pairs; legs without bristles; eyes meeting on frons.
Female: abdomen with 4 patch pairs; abdomenal segments 3 and 4 with triangular patches with indented posterior margin.

Similar species:

A similar species is Melanostoma mellinum. This is slightly smaller and usually less slender, has a shiny face and almost bald arista. In the females, the triangular patches on the abdomen have a rounded posterior margin. Melanostoma scalare may also be confused with some Platycheirus species when not looked at closely.

Biology:

Melanostoma scalare flies in several generations from March/April to September/October. It is also active in the shade and at low temperatures. Among others, the adults visit the flowers of umbelliferae, dandelion, buttercup, speedwell, various grasses, plantain species, blackthorn, holly and creeping willow. They are often found on plants that are pollinated by the wind.
Larvae of Melanostoma scalare were found mostly in the litter layer and in tussocks of grass, such as Dactylis. The larvae are mainly nocturnal and feed on small insects, such as aphids and gall midges.
Under laboratory conditions, the development from oviposition to hatching of the imagines took only 5-6 weeks. Melanostoma scalare overwinters as a full-grown larva.

References, further reading, links:

1. Pape T. & Thompson F.C. (eds) (2017). Systema Dipterorum (version 2.0, Jan 2011). In: Species 2000 & ITIS Catalogue of Life, 2017 Annual Checklist (Roskov Y., Abucay L., Orrell T., Nicolson D., Bailly N., Kirk P.M., Bourgoin T., DeWalt R.E., Decock W., De Wever A., Nieukerken E. van, Zarucchi J., Penev L., eds.). Digital resource at www.catalogueoflife.org/annual-checklist/2017. Species 2000: Naturalis, Leiden, the Netherlands. ISSN 2405-884X.
2. Gerald Bothe: Bestimmungsschlüssel für die Schwebfliegen (Diptera, Syrphidae) Deutschlands und der Niederlande, DJN, 1984, ISBN 3-923376-07-3
3. M.C.D.Speight: Species Accounts of European Syrphidae (Diptera), Glasgow 2011, Syrph the Net, the database of European Syrphidae, vol. 65, 285 pp., Syrph the Net publications, Dublin.
4. Menno Reemer, Willem Renema, Wouter van Steenis, Theo Zeegers, Aat Barendregt, John T. Smit, Mark P. van Veen, Jeroen van Steenis, Laurens van der Leij: De Nederlandse Zweefvliegen (Diptera: Syrphidae), Nederlandse Fauna 8, 2009.
5. Speight, M.C.D. & Sarthou, J.-P. (2014) StN keys for the identification of the European species of various genera of Syrphidae (Diptera) 2014 / Clés StN pour la détermination des espèces Européennes de plusieurs genres des Syrphidae (Diptères) 2014. Syrph the Net, the database of European Syrphidae, Vol. 80, 125 pp, Syrph the Net publications, Dublin